The present invention relates to resinous compositions for the prolonged release of fragrant substances. More particularly, the present invention relates to compositions of certain ethylene-vinyl acetate copolymers and one or more specific diffusing agents which, when impregnated with or enclosing a fragrant substance, provide for the uniform release of that fragrant substance over a prolonged period of time.
Fragrant compositions have heretofore been formed into aerosol, gel, liquid, powder and plastic products, of which the water-soluble gel products have found the largest commercial utility. Fragrant compositions, in a water-soluble form, which employ agar, carrageenan, gelatin, or the like as a gelling agent, are prepared by heating such a gelling agent to cause it to melt. A surfactant containing one or more fragrant substances and a dispersion aid such as methanol, ethanol, isopropanol or the like is then added to the molten gelling agent and the resulting composition cooled until it solidifies. One problem with such gel-type fragrant compositions is that the content of the fragrant substances is relatively low, generally, on the order of about 10%.
Therefore, in order to provide for the release of the fragrance over a long period of time, it is necessary to form the fragrant composition into a product of large mass. This, however, results in another problem which is that the evaporation and emission from such a large mass decreases with the passage of time because the volume decreases gradually and the gel surfaces become harder due to evaporation of water. Yet another problem with such gel-type fragrant compositions is that the fragrant substances are unavoidably subjected to heat during preparation, thereby disturbing the balance of the fragrance in the composition and, possibly, causing the fragrant substances to undergo modification.
In order to avoid these problems with water-soluble gel-type fragrant compositions, many improvements have been proposed, including, for example, avoiding the breakage of gel-type fragrant compositions by adding a thermoplastic resin to dibenzilidene or tribenzilidene sorbitol and then solidifying the resulting mixture (Japanese Patent Publication No. SHO 48-37825); obtaining a formed gel product by making use of the steam permeability and porosity of water-containing unsaturated polyester resins (Japanese Patent Publication No. SHO 52-30171); and obtaining a hydrophilic gel by reacting a peptide with a hydrophilic urethane pre-polymer (Japanese Patent Publication No. SHO 53-24492).
It is also known to employ one or more fragrant substances adsorbed on silica gel, alumina and the like. One reported improvement on this practice has been to cover each particle of powder or pulverized material, carrying one or more fragrant substances absorbed thereon, with a synthetic resin film, or mixing such powders or pulverized materials in a synthetic resin (Japanese Patent Publication Nos. SHO 43-6283, 56-4270, and 56-7423).
A number of attempts have heretofore been made to impart fragrance to synthetic resins. These attempts have, however, not been particularly successful. In general, there is no miscibility between fragrant substances and synthetic resins and, even if they are mixed together, the resultant mixture loses its effectiveness as a fragrant composition in a short period of time either because the fragrant substance oozes out onto the surface of the synthetic resin or the fragrant substance is hermetically trapped within the interior of the synthetic resin and restrained from diffusing onto the surfaces of the resin, thereby preventing the composition from releasing the fragrant substance.
By way of example, thermoplastic resins of aliphatic hydrocarbons, such as polyethylene, polypropylene and the like, have poor gas permeability while polystyrene-type and polyvinyl acetate-type resins have an extremely high gas permeability. Accordingly, none of these resins are suitably employed as a carrier for fragrant substances.
Among the many proposals that have been made to overcome the aforementioned drawbacks of such synthetic resin-based fragrant products, are employing a hydrophilic polymer of a hydrophilic acrylate or methacrylate carrier for the fragrant substance (Japanese Patent Publication No. SHO 49-4946); employing a chlorine-modified polyethylene or polypropylene coploymer (Japanese Patent Publication No. SHO 50-29015); incorporating a surfactant containing an amine compound as a penetration aid in a synthetic resin (Japanese Patent Publication No. SHO 53-1299); mixing fragrant substances in a polyolefin resin of a lower molecular weight, melting the resulting mixture, forming the molten mixture into pellets, and mixing the resultant pellets in a polyolefin resin of a high molecular weight (Japanese Patent Publication No. SHO 54-37974); and mixing fragrant substances in a coploymer of ethylene and vinyl acetate or ethylene and one of various acrylates (Japanese Patent Laid Open No. SHO 53-98352) and impregnating such copolymers with fragrant substances (Japanese Patent Laid Open No. SHO 56-121560).
The aforementioned proposals have not, however, provided fragrant compositions of any particularly satisfactory commercial value, since they require preparation of special synthetic resins for the specific uses or are limited as to the types of fragrant substances which may be employed.